Related Party Transactions (Details) $ in Thousands	1 Months Ended			2 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	May 31, 2018 USD ($) apartment	Nov. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) unit	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) investment	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($) investment	Mar. 31, 2018 USD ($)	Nov. 30, 2016 USD ($)
Related Party Transaction [Line Items]
Management and other fees from affiliates					$ 3,200	$ 2,900	$ 6,400	$ 5,900
Development and redevelopment fees					1,000	$ 600	1,900	1,400
Co-investments				$ 1,291,320	1,291,320		1,291,320		$ 1,155,984
Payments to acquire preferred equity investments							$ 97,826	$ 144,599
Equity investment, redeemed amount									5,000
Number of equity method investments scheduled to mature | investment							2
Short-term loans outstanding and due from various joint ventures				4,200	4,200		$ 4,200		5,100
Apartment Home Community In Ventura, California [Member]
Related Party Transaction [Line Items]
Commitment to fund preferred equity investment	$ 26,500
Preferred returns rate	10.25%
Commitment funded amount				20,400
Number of units acquired | apartment	400
Membership Interest In Sage At Cupertino [Member]
Related Party Transaction [Line Items]
Number of units acquired | unit			230
Co-investments											$ 15,300
Equity method investment, ownership percentage acquired			40.50%
Contract price			$ 90,000
Mortgage encumbrance											$ 52,000
Affiliated Entity [Member] | BEX III [Member] | Secured Note Receivable, 3.5% Interest Rate, Due March 9, 2018 [Member]
Related Party Transaction [Line Items]
Notes receivable		$ 29,500
Note receivable, related party, interest rate		3.50%
Limited Liability Company [Member]
Related Party Transaction [Line Items]
Payments to acquire preferred equity investments										$ 20,000
Number of preferred equity method investments acquired during period (in investments) | investment										3
Preferred stock, stated interest percentage										9.50%
Limited Liability Company [Member] | Marcus and Millichamp Company TMMC Affiliate [Member] | Secured Note Receivable, 9.5% Interest Rate, Due October 2019 [Member]
Related Party Transaction [Line Items]
Notes receivable				$ 6,600	$ 6,600		$ 6,600		$ 6,700			$ 6,600